1. Field of the Invention
The present invention relates to a manufacturing method of an adhesive tape, for example, being stuck on inner side walls of a box made of corrugated cardboard to serve as an opener or a reinforcing member of the box, and the adhesive tape manufactured by the said method. More particularly, the present invention relates to a manufacturing method of an adhesive tape having high-strength and low-elongation, and the adhesive tape manufactured by the said method.
2. Description of the Related Art
A structure of a box, for example a corrugated carton 101, is as illustrated in FIG. 2. The corrugated carton 101 has side walls 103. An adhesive tape 105 serving as an opener of the box 101 is stuck on the upper part and the inside of the side walls 103. This kind of adhesive tape 105 serving as the box opener is normally stuck on this place, that Is the upper part and the inside of the corrugated carton 101, and there are further provided cuts A along the adhesive tape 105 being stuck on the corrugated carton 101. When the corrugated carton 101 is to be opened, a person will pick up any part of the cuts A on the side wall 103, and then he will pull this part in the peripheral direction. Consequently, the part of the corrugated carton 101 will be peeled along the cuts A as well as along the adhesive tape 105 being stuck on the inner side walls of the corrugated carton 101, thus the upper part of the corrugated carton 101 is opened.
The adhesive tape 105 also serves as a reinforcing member of the corrugated carton 101.
A manufacturing method of the above discussed adhesive tape according to a prior art will be summarized as follows.
First, a film or a sheet is produced by casting or forming, and then a uniaxial or biaxial drawing is performed thereon. After that, heat treatment is performed on the film or sheet for the purpose of surface activation, and then the film or sheet is wound as to be a roll. A release agent is applied on the back surface of the film or sheet, and then the film or sheet is heated. An adhesive agent is applied on the film or sheet, and then the film or sheet is heated. Finally, the film or sheet is alit. As a result, an adhesive tape having a desired width is obtained.
The uniaxial drawing as above described means the stretching and orientating of a plastic film in one (longitudinal or lateral) direction at a temperature between the melting point and the second order transition point of the plastic film. The biaxial drawing as above described means the stretching and orientation of a plastic film in two (longitudinal and lateral) directions at a temperature between the melting point and the second order transition point of the plastic film.
However, the prior art manufacturing method of an adhesive tape as above discussed has the following disadvantageous points.
First, in the thus obtained adhesive tape as the final product, there exists longitudinal crack or fuzz. This problem is caused due to occurrence of fiberization of the film or sheet. In addition, the manufacturing of the prior art adhesive tape as above discussed requires a large-sized production facility, which would result in higher production cost.
Further, slitting or cutting of the fiberized film or sheet (in order to obtain an adhesive tape of a desired width) provides more remarkably longitudinal crack or fuzz because the fiberized film or sheet is slit in the perpendicular direction with respect to the fiberized direction, whereby the fiber is cut.
Second, there still remains some residual volatile component of the adhesive agent after the applied adhesive agent has been heat-dried. When the adhesive tape is used, this residual component is volatized while giving off a foul smell. This problem is caused due to insufficient heating and drying of the film or sheet after application of the adhesive agent.
In the light of problems which have been described as above, the object of the present invention is to provide a manufacturing method of an adhesive tape which is free from longitudinal crack or fuzz, with no residual volatile component (derived from an adhesive agent) in a small-sized facility.
For the object as above discussed, according to a first embodiment of the present invention, there is provided a manufacturing method of adhesive tape, comprising steps of: preparing a raw material of a biaxially or non- drawn, film or sheet on the back surface of which a release agent has been applied and to the which an adhesive agent has been applied, and subjecting the raw material to uniaxial drawing under heated conditions without deteriorating releasing and adhesive performance of the raw material, thus producing a base material of an adhesive tape having high-strength and low-elongation.
According to a second embodiment of the invention, there is provided the manufacturing method of an adhesive tape as described above, further comprising a post-heat treatment step of heating the drawn material, the uniaxial drawing step and the post-heat treatment step involving heating the release agent and the adhesive agent sufficiently to complete their cure reactions as well as to remove a volatile component of the adhesive agent, which otherwise would volatile and give off a foul smell in use.
According to a third embodiment of the invention, there is provided the manufacturing method of an adhesive tape according to the first embodiment of the invention, in which the uniaxial drawing step is performed under drawing conditions where width, thickness, draw ratio, temperature, speed and period of time are so set suitably in given ranges that a resultant adhesive tape will possess desired width, thickness, strength and elongation.
According to a fourth embodiment of the invention, there is provided the manufacturing method of adhesive tape according to the first embodiment of the invention, further comprising a step of slitting of the raw material at a predetermined width before the uniaxial drawing step.
According to a fifth embodiment of the invention, there is provided an adhesive tape manufactured by steps of: preparing a raw material of a biaxially or non- drawn, film or sheet on the back surface of which a release agent has been applied and to the which an adhesive agent has been applied, and subjecting the raw material to uniaxial drawing under heated conditions without deteriorating releasing and adhesive performance of the raw material, thus producing a base material of an adhesive tape having high-strength and low-elongation.
According to a sixth embodiment of the invention, there is provided the adhesive tape as described above, wherein long and narrow bubbles elongated in the direction of the uniaxial drawing are seen on the adhesive tape.
The inventive manufacturing method is characterized by preparing a raw material of a biaxially drawn film or sheet on the back surface of which a release agent has been applied and to the which an adhesive agent has been applied, and subjecting the raw material to uniaxial drawing under heated conditions without deteriorating releasing and adhesive performance of the raw material. Consequently, the method inhibits the fiberization and requires no facility required for steps ranging from casting, forming to applying adhesive agent.
If the post-heat treatment is subjected to the drawn material, heating during the uniaxial drawing step and the post-heat treatment step can complete the curing reaction of the release agent and the adhesive agent. In addition to the completion of the reaction of the release agent and the adhesive agent, some volatile component of the adhesive agent can be removed, which would otherwise volatize and give off a foul smell in use.
The uniaxial drawing conditions, that is, width, thickness, drawrate, temperature, speed and period of time can be so set suitably in given ranges that a resultant adhesive tape will possess desired width, thickness, strength and elongation.
Further, slitting the raw material in the width direction may be done, prior to the uniaxial drawing step.
During application of the adhesive agent, an extremly small amount of bubbles are inevitably mixed in the applied coat due to volatilization of the adhesive agent, etc. In the prior art method in which an adhesive agent is applied after uniaxial drawing has been performed, each of these bubbles has spherical shape (that is, the shape of bubble as it is), which is substantially the same as illustrated in FIG. 3. However, according to the present invention in which uniaxial drawing is performed after an adhesive agent has been applied, each of the bubbles is extended in the direction of the uniaxial drawing, or long and narrow, as illustrated in FIG. 4 (in the present case, the drawing is performed at a draw rate of about 2.7 times). That is to say, uniaxial drawing changes the bubbles from the FIG. 3 shape to the FIG. 4 shape.
Therefore, the adhesive tape manufactured according to the present invention can graphically be characterized in that the long and narrow bubbles elongated in the direction of the uniaxial drawing are seen on the adhesive tape.